The present invention relates to an exposure apparatus for transferring a pattern formed on one member to another member, particularly to an exposure apparatus wherein a semiconductor wafer is exposed to a pattern of an IC circuit formed on a reticle or a mask.
An apparatus of this type is known, for example, as a stepper wherein an IC circuit pattern formed on a reticle or a mask (hereinafter called simply a "mask") is projected onto a semiconductor wafer through a projection lens; the wafer is stepped for the next pattern projection; and these operations are repeated to expose a plurality of wafer portions to the pattern.
A typical example of this apparatus is shown in FIG. 1, wherein the apparatus comprises a frame 5 and a lens support 4 which is supported by the frame 5 and which supports a projection lens (not shown). A mask 1 is fixed in alignment with a reference 3 fixed on the frame 5 or the lens support 4. The apparatus further comprises a wafer stage 7 which supports a wafer 6 for movement in orthogonal directions (X and Y) directions. In order to regulate the step movement of the wafer 6 by the wafer stage 7, the change in the relative position between the wafer stage 7 and the lens support 4 is detected by a distance measuring system utilizing a laser interferometer. More particularly, a first mirror 10 is fixed to the lens support 4, while a second mirror 11 is fixed to the wafer stage 7. In association with these mirrors 10 and 11, a laser interferometer is provided, which includes a beam bender 20, a laser source 21, a detector 22 and an interferometer 23 affixed on a base 12. The laser beam produced by the laser source 21 is divided by the interferometer 23 into two beams in different directions. The respective beams reciprocate through a first and second optical systems which is constituted by the mirrors 10 and 11, respectively. Because of the optical path difference for the respective beams, a phase difference results and is detected by the detector 22. Thus, the amount of stage movement can be determined.